The subject invention relates in general to a load management system for use in commercial electrical power distributor systems. In particular, it deals with the art of controlling the distribution of power service to the constituent loads of an electrical distribution transformer to thereby reduce the transformer load during periods of peak electrical demand. This control function is achieved in part by a unique application of our prior invention ("Meter Apparatus Having Logarithmic Response to Current and a Linear Response to Temperature") as described in U.S. Pat. No. 3,398,368, and serves to reduce power demand during peak periods by deferring a portion of the power service supplied to lesser priority customer loads until such time as the peak demand subsides.
The high quality and plentiful supply of electrical power service became commonplace several years ago. Its low cost was largely due to the availability of an ample supply of low cost fuel and load building programs which resulted in high load factors. Historically, the power service industry has been able to forecast its potential load growth five to ten years in advance thereby allowing adequate lead time to increase production capacity to meet expected demands.
Within the last few years, however, the electric power service industries have been presented with a number of problems which threaten the established pattern of plentiful supply at relatively low cost. For example, the widespread and rapidly growing use on the part of residential customers of higher wattage appliances and intermittently operated convenience equipment is creating an acute shortage of system capacity for many electric utilities. The increasing use of air conditioning equipment is a prime example. In the past, peak demand periods were created principally by customers' use of electric lights. Therefore, the peaks ordinarily occurred between nightfall and midnight, and were most pronounced in the winter evenings. In many areas this situation has undergone an almost complete reversal, and the cooling load has now become by far the largest contributing factor. Major peaks now tend to occur in the hottest days of summer rather than in winter, and usually in the late afternoon rather than after the cool of nightfall. Moreover, the cooling demand normally occurs at times when the higher summer temperatures decrease the output potential of power generation equipment.
The cooling load demands large blocks of kilowatt generating capacity but consumes few kilowatt-hours in proportion to its high (almost 100%) contribution to peak system loading. Electric utilities must therefore commit unusually large capital investments for power generation in support of seasonal demand peaks. Unfortunately, electrical energy generally cannot be stored but must be manufactured, delivered and used instantly; consequently, billions of dollars worth of electric utility system capacity is idle (during off-peak periods) more than fifty percent of the time. Nevertheless, in many areas where system capacity goes unused a portion of the time during off-peak periods, utility networks are forced to increase generation capacity to meet peak demands. This additional capacity must be provided by new generating plants whose construction typically requires five to ten years or by gas turbine installations which can be made operational in twenty-four months. Although large capital investments are needed to construct traditional generation plants, this method of power generation utilizes relatively abundant fuels and operates fairly efficiently. In contrast, gas turbine generation requires a smaller capital outlay but requires the use of scarce fuel and is relatively inefficient.
Electric energy conservation programs now in practice reduce kilowatt-hours but do not reduce kilowatts of "demand" in the same proportion. This tends to lower the annual load factor which in turn increases kilowatt-hour costs. In fact, the conservation of kilowatt-hours of energy may be secondary to the conservation of kilowatts of "demand." However, by reducing peak loads and shifting energy demands to the valleys of the load curve, system capacity could be released and generation costs lowered.
Our invention provides a unique means for overcoming the aforementioned problems. In particular, our invention interrupts the distribution of power to a portion of the peak load in order to decrease the overall peak demand. The load deferral function is controlled by a power monitor which is located at the distribution transformer. Placement of the power monitor at the distribution transformer is advantageous because it is here that the individual customers' peaks merge into coincident peaks which normally correspond with the peak of the overall network. In any event, control at the distribution level using our invention releases capacity throughout the entire system. To our knowledge, the prior art does not teach load control at the distribution transformer to effect such a load management function.
The subject invention provides a load management system reducing peak loads in electrical power supply networks. The disclosed power monitor senses transformer current flow and produces a logarithmic current flow in an associated resistive electrical circuit comprised of a bimetal spiral coil. The heating effect caused by the induced current flow combined with the ambient temperature of the system produces a rotational response in the bimetal spiral coil related to the effective load on the transformer. Rotation of the bimetal spiral coil in response to an increasing transformer load closes the contacts of a control switch which activates the load deferral function of the present invention. Rotation of the bimetal spiral coil also causes the control switch to rotate to a point representative of the peak load on the transformer.
The maximum control switch setting is mechanically preserved by a rachet device and is thereafter used as an upper system control point. Once the upper system control point has been set, subsequent transformer loading drives the bimetal spiral toward the upper control point and closes the control switch when the control point is reached. If the transformer uncontrolled load increases above the previous peak, the control switch is rotated to a new point corresponding to the increased peak load thereby establishing a new upper level control point. In this way the power motor device of our invention is self setting and switching of the controlled load always occurs at a peak that has been established by the uncontrolled load.
Closure of the control switch causes complete interruption of electrical service to a number of the controlled loads served by the transformer called the deferrable loads and activates a motorized cam driven timing device. The motorized cams operate on switching means to selectively interrupt electrical service for preselected time intervals to a second group of loads called the cyclical loads, thereby cycling the service supplied to these loads. The contractive rotation of the bimetal spiral in response to a decreasing transformer load opens the contacts of the control switch restoring uninterrupted service to all of the cyclical and deferrable loads. A variation of the invention provides a lower system control point to control a third plurality of controlled loads. When transformer loading decreases sufficiently to activate the lower level control switch, electrical service from the transformer is provided to a third group of loads which comprises low priority loads not demanding at least partial service during periods of relatively high transformer loading.
An alternate embodiment of the present invention includes a signal generator and receiver for sending and receiving high frequency control signals over ordinary power distribution lines to activate the above described load deferral function. The use of high frequency control signals to cycle, defer and record the peak load provides two additional control options. First, a signal generator capable of sending a universal control signal can be used by the dispatcher of a power company to remotely initiate the load deferral function of each power monitor in the system. Second, the control signal can be provided by the dispatcher to sensors at each distribution transformer which in turn sends a repeat signal to remove preselected loads from the system during periods of peak demand.
It is therefore an object of the present invention to provide a unique method and apparatus for controlling peak loads in electrical power supply networks.
A further object of the present invention is to provide a unique method and apparatus for reducing the peak load in a power supply network by completely interrupting electrical service to a first group of controlled loads and by cycling electrical service to a second group of controlled loads. Reduction of the network peak load effectively increases the capacity of the network thereby increasing the efficiency of the network's supply equipment.
A further object of the present invention is to provide a unique method and apparatus that can control certain constituent loads served by an electrical distribution transformer to thereby reduce a portion of the peak demand placed on said transformer. It is a feature of this invention that the power monitor device can be easily and rapidly mounted in proximity to the distribution transformer without interrupting power service to the customer.
Another object of the present invention is to provide a unique method and apparatus for automatically controlling the peak load in a power supply network by means of a self-setting control mechanism that does not require continuous monitoring.
Another object of the present invention is to provide a unique method and apparatus that is operable to provide a load management function at the individual transformer level in order to increase the annual load factor on the associated power supply network.
A further object of the present invention is to provide a unique method and apparatus that is operable to identify and record the magnitude of an electric utility customer's contribution to the peak load. By assessing each customer's responsibility for the peak load, a cost base pricing system may be established wherein each customer will be charged in relation to their contribution to the peak load.
Another object of the present invention is to provide a unique method and apparatus that is operable to inhibit electrical power service to selected loads served by a particular distribution transformer to periods when the transformer load is relatively low.
Another object of the present invention is to provide a unique method and apparatus that can control the peak load in a power network by means of incremental load deferral so that a smoother control of these loads can be obtained.